The present invention refers to a clamping apparatus with a clamping chuck and a work piece carrier having a clamping pin. Particularly, the apparatus of the invention comprises a clamping chuck and a work piece carrier adapted to be releasably connected to the clamping chuck, the work piece carrier having a flat bottom surface and comprises a clamping pin protruding from the flat bottom surface.
The clamping chuck is provided with a central opening for receiving the clamping pin of the work piece carrier, the central opening having a conical inserting portion, and a clamping mechanism for clampingly fixing the clamping pin of the work piece carrier in the central opening of the clamping chuck.
Such a clamping apparatus is preferably used for clamping work piece carriers equipped with one or several work pieces to be machined in the machining area of a machine tool in a well-defined and predetermined position. Usually, the clamping chuck of the apparatus is fixed in the machining area of the machine tool, while the work piece carrier, provided with a clamping pin, is releasably attached to the clamping chuck.
In order to be in a position to clamp work pieces with different dimensions, so-called palletizing systems are known which comprise a plurality of clamping chucks, usually two, four, six or eight of them. By means of these plurality of clamping chucks, a work piece carrier equipped with, depending on its size, two, four, six or eight clamping pins can be clamped. In certain cases, it may happen that the work piece carrier is equipped with an odd number of clamping pins. Since an individual clamping chuck usually comprises neither means to avoid a rotation of the clamping pin nor means for determining the angular position of the clamping pin around the Z-axis, it can be advantageous to provide one or several clamping chucks with positioning means, determining besides the X- and Y-positions also the angular position around the Z-axis, with the result that, if appropriate, also work piece carriers having but one clamping pin can be clamped to the clamping chuck in an exactly defined linear and angular position. It is understood that in such a case also the work piece carrier has to be provided with positioning means cooperating with the above mentioned positioning means of the clamping chuck.
The accuracy of the relative position between work piece carrier and clamping chuck can be severely impaired particularly by contamination of the elements of the apparatus responsible for the fine positioning. Predominantly in the case of conical centering and positioning surfaces, respectively, there is a danger that dirt particles adhere to or are deposited on the conical inserting portion and/or the conically shaped aligning surface of the clamping pin.
The document DE 41 10 857 discloses an apparatus for coupling a tool holder to a working spindle of a machine tool. The working spindle is provided with an opening for receiving a shaft portion of the tool holder. The opening has an upper and a lower conical portion with an annular recess having a supporting surface located between the two conical portions. The shaft portion of the tool holder is equipped with two cone rings supported by elastic abutments. Between the two cone rings, a locking mechanism is located, comprising two radially movable locking pieces. On the top, these locking pieces are provided with wedge shaped surface areas that rest in the locked state on the supporting surface of the annular recess. By providing the elastic abutments, the cone rings are axially movable relative to the shaft portion of the tool holder and enable the shaft portion to be pulled in into the opening after the cone rings having been rested on the conical portions of the opening. The cone rings themselves are provided with slots. The shaft portion is provided with a flange portion constituting at its lower end a flat annular surface serving as a Z-direction stop member, resting on the front face of the working spindle upon clamping the shaft portion. In the opening of the working spindle, both conventional clamping pins (FIG. 5) and sectional clamping pins (FIGS. 1 and 3) can be clamped. Thus, the basic idea of that invention may be seen in the fact that work piece carriers with differently designed clamping pins can be clamped by the working spindle of the machine tool. It is understood that such a clamping apparatus is not at all suitable for attaching a work piece holder to the working spindle of a machine tool in a highly accurate and repeatable manner.
U.S. Pat. No. 5,961,261 discloses a clamping system with a clamping cylinder for pulling-in and clamping a pull-in nipple. The clamping cylinder is provided with a central bore for receiving the pull-in nipple. The nipple itself is provided with centering surfaces to ensure proper positioning inside the central bore of the cylinder. Additionally, it is provided with at least one cutting means, in the form of a cutting surface or a cutting edge. Should any chips stick to the nipple or to the centering surfaces of the cylinder, these chips are cut and removed. The cutting means on the nipple may be extending radially and comprising several independent cutting edges, or may be extending circumferentially. The clamping cylinder is provided with a plurality of uniformly distributed gas outlet openings, leading into free spaces between the cutting edges. By providing these free spaces, the region in front of the outlet openings 14, 15 shall be kept free of dirt particles, thereby avoiding a contamination of the outlet openings. In the region of the centering surfaces, however, no gas outlet openings are provided.
U.S. Pat. No. 5,415,384 discloses an apparatus for clamping a work piece at a workstation of a machining apparatus in a well-defined position. The apparatus comprises a base and a work piece carrier adapted to be put onto and fixed to the base. The base is provided with four centering rulers, engaging in each case a plate member provided with a groove and being elastically resilient in Z-direction in order to align the work piece carrier in X- and Y-directions. For clamping the work piece carrier to the base, separate clamping pins are provided which, however, do not have any centering or aligning function.
Finally, German patent document DE 200 21 407 discloses a clamping apparatus for fixing a pull-in bolt on a machine table. This clamping apparatus comprises a base plate, having a piston inserted into it, covered by a cover plate screwed to the base plate. The top surface of the cover plate comprises seat portions serving as Z-stop members. The base plate is provided with air channels, centrally opening into the seat portions and adapted to clean the surfaces thereof.
It is an object of the present invention to provide an improved clamping apparatus comprising a clamping chuck and a work piece carrier adapted to be releasably connected to the clamping chuck in which the surface areas responsible for the accuracy of the relative position between work piece carrier and clamping chuck are easily kept free of contamination.
In order to meet this and other objects, the present invention provides a clamping apparatus, comprising a clamping chuck and a work piece carrier adapted to be releasably connected to the clamping chuck. The work piece carrier has a flat bottom surface and comprises a clamping pin protruding from the flat bottom surface.
The clamping chuck has a central opening for receiving the clamping pin of the work piece carrier with a conical inserting portion and a clamping mechanism for clampingly fixing the clamping pin of the work piece carrier in the central opening. The clamping pin comprises a rear section adjacent to the flat bottom surface of the work piece carrier, having several exposed surface portions adapted to engage the conical inserting portion of the central opening for aligning the position of the clamping pin in X- and/or in Y-directions.
Moreover, the clamping chuck is provided with gas outlet openings located in the conical inserting portion of the central opening for blowing a gaseous medium against the exposed surface portions to thereby clean the surfaces thereof upon inserting the clamping pin into the central opening of the clamping chuck.
Thus, one of the basic ideas of the present invention is to ensure a fine positioning of the clamping pin not by means of large positioning surfaces, but to provide the clamping pin with a number of small, exposed aligning surface portions having but a limited extension, by means of which the clamping pin is accurately aligned in X- and/or Y-directions at the conical inserting portion of the central opening in the clamping chuck. These small exposed aligning surface portions can easily be kept clean by blowing air or another gaseous medium out of openings provided at corresponding locations in the conical inserting portion. Since these aligning portions both are exposed and of small dimensions, blowing pressurized air there against ensures a thorough and very efficient cleaning.